1. Field of the Invention
The present invention relates to a multi-output DC/DC converter, and more particularly, to a multi-output DC/DC converter capable of controlling power-conversion switching in synchronization with a frequency of one output voltage among multiple output voltages in an LLC resonant DC/DC converter.
2. Description of the Related Art
Power supplies, particularly, DC/DC converters have been commonly used for information devices such as personal computers, and home electronic appliances such as air-conditioners and audio-visual devices.
The DC/DC converter may provide multiple output voltages according to an electronic product to which the DC/DC converter is applied.
A general multi-output DC/DC converter converts an input DC voltage to an AC voltage through a single transformer, and rectifies the converted AC voltage to output multiple DC voltages. However, if a voltage level of one DC voltage among multiple DC voltages is changed by a single transformer, it affects to other DC voltages, causing the general multi-output DC/DC converter to fail to maintain cross-regulation. In order to maintain the cross-regulation, a multi-output DC/DC converter employs a buck chopper circuit at an output terminal.
FIG. 1 is a diagram illustrating a configuration of a related art multi-output DC/DC converter.
Referring to FIG. 1, in the related art multi-output DC/DC converter, a switching unit 11 converts an input DC voltage Vin into an AC voltage by alternate switching, and sends the converted AC voltage to a primary winding L1 of a single transformer 12.
First and second secondary windings L2 and L3 respectively send AC voltages to first and second rectification units 13 and 14 depending on the preset ratio of the number of turns of the primary winding L1 to the corresponding secondary winding. The first and second rectification units 13 and 14 rectify the AC voltages to output DC voltages.
In detail, the first rectification unit 13 outputs a first DC voltage Vs, and the second rectification unit 14 sends a DC voltage to a buck chopper circuit 15. The buck chopper circuit 15 switches the DC voltage from the second rectification unit 14 under the control of a controller 15a, and outputs a second DC voltage Va having a lower voltage level than a voltage level of the DC voltage.
The buck chopper circuit 15 includes a switch S, a freewheeling diode D, and a filter L.
However, the related art multi-output DC/DC converter has a limitation of low power conversion efficiency because it performs primary voltage conversion and then re-converts the voltage through the buck chopper circuit 15. Also, the buck chopper circuit 15 causes an increase in number of components, thereby increasing a manufacturing cost.